UPDATE – WATER LEVELS IN NONACHO LAKE STABILIZING
July 7, 2021
It appears that water levels in Nonacho Lake have peaked and are now beginning to stabilize. On June 18, NTPC opened two gates at the Nonacho Lake Dam to attempt to keep water levels in Nonacho Lake within the parameters of its Type A Water Licence for the Taltson Hydro Facility. The gates were designed to provide flow to the Taltson hydroelectric facility during low water periods while the Pine Point Mine was operating – they were not designed to offset high natural inflow to the reservoir.
Opening both gates only resulted in the addition of approximately 5% to the total flow in the Taltson River. Despite opening the gates, the upper water level limit of 321.6m for Nonacho Lake was exceeded as of July 1, 2021. The maximum daily level recorded in provisional data has been 321.64m.
Although water levels in the lake seem to be stabilizing, they remain slightly above the limit at 321.63m. NTPC has notified the Mackenzie Valley Land and Water Board, GNWT Department of Environment and Natural Resources Water Licence Inspectors and local stakeholders about the water licence exceedance and will continue to closely monitor water levels in Nonacho Lake and on the Taltson River downstream of the hydroelectric facility.
June 18, 2021
NTPC has opened two gates at the Nonacho Lake Dam to keep water levels in Nonacho Lake within the parameters of its Type A Water Licence for the Taltson Hydro Facility - MV2011L4-0002. There are three small gates at the Nonacho Lake Dam which can be used to release water from Nonacho Lake into the Taltson River system primarily during low water years but they can also be used when water levels in the lake get too high. The gates have been closed since 2014.
Based on current monitoring data in the Taltson River, two open gates will add just over 5% to the total river flow. The high-water levels currently being observed in the river are caused by a number of factors, primarily natural precipitation and snow melt. Overflow from the Tazin River is significantly higher than has ever been recorded before. In a normal year, the Tazin River is not a major contributor to the overall volume of water in the Taltson River system. In 2020 and 2021, however, the Tazin has been a major contributor, sometimes responsible for as much as 80% of inflows. The additional water being added through the gates at Nonacho Lake will not have a significant impact on downstream water levels
The Nonacho Dam is located 160 kilometres upstream of the Taltson Hydroelectric Facility and 300 kilometres upstream of the Taltson River outlet into Great Slave Lake.
ORIGINAL POSTING
June 4, 2021
NTPC anticipates that it will be opening one or two gates at the Nonacho Lake Dam within the next two weeks in order to keep water levels in Nonacho Lake within the parameters of its Type A Water Licence for the Taltson Hydro Facility- MV2011L4-0002. Opening of the gates could occur as early as next week or be delayed until later in the month, with this decision based on fluctuating water levels on Nonacho Lake and the Taltson River.
Water levels in Nonacho Lake have recently been rising and are approaching the permitted limits. This is a situation that changes daily along with the weather and has to be managed on an ongoing basis, making it difficult to state a specific day or time when the gates will be opened. Opening the gates results in additional water entering the Taltson River system.
NTPC has estimated that water volume in the Taltson River will increase by approximately 4 percent per gate. It is unclear at this time whether one or two gates will need to be opened. Based on current water levels in the Taltson River, neither option poses a risk of flooding for downstream property owners. NTPC is monitoring water levels in the Taltson River system including Nonacho Lake and will time the gate opening to strike the best possible balance between managing water levels on Nonacho Lake and water levels on the Taltson River
NTPC has not been required to open these gates since 2014. When the Pine Point Mine was operating, the gates were opened and closed as required to ensure water levels downstream at the Taltson Hydroelectric Facility were sufficient to meet electricity demand. Since Pine Point closed, electricity demand in the South Slave has dropped and NTPC only operates the gates when required to maintain compliance with its water licence. Water management activities do not relate directly to electricity generation.
NTPC will provide updates on this situation as events progress.